Manufacture of double-walled vacuum receptacles



Dec. 10, 1929.

MANUFACTURE OF DOUBLE WALLED VACUUM RECEPTAGLES c. G. FINK ET AL.1,738,991

Filed NOV. 24, 1925 r INVENTORS /0 COL/N 6 51M fo/m 8.555%;

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Patented Dec. 10, 1929 UNITED STATES PATENT OFFICE COLIN G. FINK ANDJOHN R. BEERS, OF N EW YORK, N. Y., ASSIGNORS TO THE AMERI- CAN THERMOSBOTTLE COMPANY, OF MARYLAND NORWICH, CONNECTICUT, A CORPORATION 01MANUFACTURE OF DOUBLE -WALLED VACUUM RECEPTACLES Application filedNovember 24, 1925. Serial No. 71,207.

Our invention relates generally 'to the manufacture of vacuum vessels ofthe wellknown double-Walled type employing two containers spaced by anannular vacuum chamber. These containers are usually of glass, and theinside walls of the vacuum chamber are silvered to prevent loss of heatby radiation from the contents of the inner container. It is the objectof our invention to provide novel methods and means for coating thedouble walls of the vacuum chamber with a metallic mirror-like surface.I

In the manufacture of vacuum bottles of the type referred to, theprocess of silvering heretofore employed is a wet process and consistsin depositing a silver coating on the glass walls by precipitation froma solution of silver nitrate, pumping out the remaining solution, andthoroughly rinsing the silvered surfaces with cold water. The bottlethen must be baked in an oven for several hours all to give the silver apermanent set and to dry the silvered chamber as much as possible before evacuatingthe same. These operations require a silvering departmentand a drying department. Now, while the baking does set the precipitatedsilver, it does not remove all moisture from the chamber, owing to theconstricted tubular path through which the steam must slowly escape. Thepresence of moisture in the space to be evacuated has always been thecause of serious troubles and difficulties in the manufacture of vacuumbottles. It has been absolutely impossible. under this wet silveringprocess, to get rid of all moisture in the vacuum chamber, because thismoisture clings tenaciously to the precipitated silver, particularly incorners and crevices where the precipitation is thick, and it also getsinto the asbestos spacing pads arranged between the two containers.Asbestos being fibrous, moisture remains occluded in these pads evenafter the long baking operation. $0 that, the presence of moisture inthe vacuum space must always be reckoned with during these vacuumoperations. This moisture interferes with securing a proper degree ofvacuum and thereby greatly reduces the heatinsulating efficiency of thebottle. Moreover, moisture in the evacuated space gets into the exhaustpumps and makes frequent cleaning of the same necessary. Also, it is acommon experience that the presence of moisture in the vacuum chamberfrequently causes the bottles to break. Then, too, the silver solutionsare expensive. Obviously, all these factors in the prior 'wet silveringprocess concient in producing the re uired metallic coating on theinside walls of the vacuum chamber. To this end, we arrange a closedcoil or cage, as it may be called, of a suitable volatile metal aroundthe inner container in the chamber to be evacuated. Asa practicalexample of such a metal, we may mention magnesium, which we havesuccessfully employed. The bottle, with the volatile wire properlyarranged in the annular space between the two containers, is then heatedto a high tempera ture and simultaneouslyevacuated to the requireddegree. Surrounding the bottle is a high-frequency coil, which inducessecondary currents in the closed wire in the vacuum chamber, and theheat generated by these induced currents volatilizes the metal of thewire, causingthe same to be deposited on the surrounding walls as auniform mirror-like 1 coating. This deposition of the metal may occurwhile the bottle is still connected to the exhaust pump or after theevacuated chamber is sealed. It requires only a few seconds to heat thewire to vaporization temperature, and the metallic coating thus producedis instantly permanent without the need of fun ther treatment. Theprocess being entirely dry, all previous difiiculties due to the presence of moisture are completely eliminated.

in order that those skilled in this art may understand our inventionfully and clearly, we shall describe a preferred form of pro cedure incarrying our ideas into effect, without intending the described detailsas limitations of our invention. Although our new silvering process isindependent of any par ticular apparatus, the diagrammatic illustrationsin the-accompanying drawings will be helpful in ex laining the inventionand its advantages. these drawin Fig. 1 shows a double-walled glassfiller partly in'seetion, containing a coil or ca e of mirror-formingwire in the annular 0 amber between the two containers;

Fig. 2 is a QIOSSrSOCt/IOII on line 2-2 of Fig. 1; o

ig. 3 is a fragmentary view on an exaggerated scale to indicate roughlyhow the spacing pads between the two containers are Y held in place bythe metallic coating; and

outer container and B the inner container which holds the liquid or foodtobe kept hot or cold. It has been customary to blow these containers.as se arate cylinders, which are later united by using them togetheraround the neck, as indicated at 10. The two containersare separated byan annular chamber C of practically uniform width. This chamber is subseuently exhausted and thus forms a heat-insu atingvacuum space around theinner container, thereby retaining the contents of the bottle foraconsiderable time at the temperature at which they were put in. In orderto prevent, or at least minimize, loss of heat from the inner containerby radiation across the vacuum space, manufacturers of vacuum .bottleshave for many years silvered the inner surface of-the outer containerand the outer surface of the inner container. These bright mirroredwalls reflect radiant heat rather than absorb or transmit it. The wetprecipitation process heretofore employed in silvering the walls of thevacuum space has alreadybeen mentioned, and we shall now describe indetail our new process for depositing a mirror coating on the surfaces12'and 13 of vacuum chamber 0.

While the outer cylinder A is still open at the base, as roughlyindicated by dotted lines 14, we insert into space C as closed coil orbasket D of a suitable volatile metal, so

.- arranged'as to extend practically along the 55 entire length of theinner container. In our experiments we secured very satisfactoryresultswith a pure magnesium wire of from 20 to mils in diameter, with theturns about one-half inch apart. The ends of the coil are preferablyconnected to the different turns, as shown at 15, to provide in effect aplurality of short-circuited coils for; a purpose that will a pearlater. The wire cage or basket D is sliown in Fig. 1 as formed in twosections, a main section (1 and a neck section d". This is merely forthe mechanical convenience of inserting the ca e into the vacuumchamber. The neck sectlon d, which consists of a few turns of wire, isplaced around the neck of the inner container before the two cylindersare fused together at 10. After the two containers have been joined atthe neck into a unit, with the coil section at in place, and while theouter member A is still 0 en at the base, the main coil section (1 issipped over the inner member B. We ob tained the best results by formingthe wire cage D of such a size that the turns fit loosely over the innercontainer and lie between the adjacent surfaces 12 and 13. This s acingof the wire not only makes it easy to s ip the cage or basket in place,but it seems to cause a more uniform coating of magnesium on the'surrounding walls. a At least, such has been our experience, but wewant to make it plain that our invention is not limited in thisparticular.

After the cage D has been partially inserted over the inner container B,suitable spacing ads 16 are placed on the inner container etween theturns of wire. As the cage is then pushed in completely, the pads 16 arecarried along into the chamber 0, as indieated in Fig. 1. These spacingpads are preferably of heat-insulating and shockabsorbing material (e.g., asbestos), and are properly spaced around the annular chamber C tosupport the inner container laterally against shocks and strains.

After the cage D has been properly inserted into chamber C, the bottom17 is formed on the outer container A. The assembled bottle is nowsuitably supported for the exhausting and silvering operations. As nospecial form of support is necessary, we need not show or describe thisdetail. In practice we found it convenient to support the bottle at theneck in upright inverted position. By means of a tubular extension 18,the bottle is connected to a suitable exhaust pump, as will beunderstood without further explanation. The bottle is surrounded by aprimary coil E connected with a source of high-frequency currents, adiagrammatically indicated at 19, which is intended to represent anypractical apparatus for generatin alternating currents of highfrequency. y way of example, we might mention that we have used acircuit employing the standard -watt pliotron power tubes as anoscillation control, and we have also used a circuit with a series ofspark gaps and condensers to obtain high frequencles.

We shall now suppose that the completely assembled filler is properlysupported within the primary coil E and is connected to a Y vacuum pump.External heat is now applied to the bottle so as to heat the same to thehighest temperature which the glass will safely stand under pressure.The exhausting operation is carried on while the glass is maintained athigh temperature, which is ordinarily around 400 (1., until the desireddegree of vacuum in chamber C has been obtained; The condition of thevacuum'may be tested in any practical way, as by mean of a high-tensionbrush discharge. When,by this test,no visible discharge can be noticedthrough the space 0 while under evacuation, the external heating isdiscontinued and the circuit through coil E is closed. At this time, thebottle may remain attached to the pump, or the vacuum in chamber C maseconds, after t e hi h-frequency coil E is connected in circuit, t ecoil D in the vacuum chamber becomes so highly heated by the inducedsecondary currents therein that the metal of the wire vaporizes andsublimes,

being deposited on the surrounding walls 12 and 13 in a substantiallyuniform coating. l/Vhen magnesium is used for the wire of coil D, themetallic coating thus formed is a bright silvery mirror-like surface. Infact, it is very ditlicult to distinguish this magnesium mirror from oneof pure silver. In Fig. 3, the deposited metal coating is indicated. atF with exaggerated thickness. By forming and arranging the volatile coilD in such a way that the turns of wire extend practically over the fulllength of chamber C, the volatilized metal is distributed over theentire inner walls of the vacuum chamber, covering them completely (orpractially so) with a clear metallic mirror of approximately uniformthickness. This mirror remains permanently fixed on the glass Withoutfurther treatment. If the bottle is left connected to the exhaust pumpduring the heating of coil D by inductive action from primary coil E,the bottle is sealed when the mirror has been formed.

After the wire cage D has been partially or completely dissipated andtransformed into a mirror, the pads 16 are held in place by thesurrounding layer of deposited metal. This will be understood from Fig.3. Even though the coating F is very thin, it nevertheless hasappreciable thickness and serves to retain the pads 16 againstdisplacement by ordinary shocks or ars. The metallic mirror does notcover the small round areas where the pads 16 press against the glass,but that does not interfere with the usefulness of the mirroredsurfaces. Hence, when we refer to the de posited coating as completelycovering the walls of the vacuum chamber, allowance must be made for thespacing pads and for such irregularities as may occur in the mirroredsurface in spite of all precautions. In processes of this nature, it isnot always possible in practice to obtain perfect results even under thebest conditions.

Instead of using separate pads 16 placed between the turns of wire coilD, we may use spacers in the form of beads or buttons of magnesium (orsimilar metal) strung di be sealed. Within a few rectly on the wire.After the deposit of the volatile wire on the vacuum walls, thesespacing beads are held securely in position b the mirror surfaces F,like the pads 16 in f g. 3. By coating the metal spacing beads with afilm of oxide, it is possible to reduce their heat conductivity to suchan extent as to minimize loss of heat due to conduction from the innerto the outer container. The shape of the wire cage D will obviouslydepend upon the particular. size and shape of the bottle. At the presenttime we prefer to make this coil with the cross-'connections 15, becausethis construction provides a plurality of short-circuited turns orwindings which facilitate and make more uniform the heating of the cageby the induced secondary currents. Thiswill be understood by those whoare familiar with the action of high frequency currents in closedconductors. By rapidly and uniformly heating the wire cage D to itsvaporization temperature, the metal is distilled and deposited on thewalls of the vacuum chamber in a clear bright mirror.

The heating coil E should be of such length I and diameter that theinduced magnetic field will have its greatest strength in those regionswhere it is cut by the Wire cage D, so that the secondary currents incoil D will produce maximum heating effect. Precaution must be taken notto vaporize the metal of coil D too rapidly, as this would cause a dullplating on the glass due to the deposit of relatively large particles ofmetal instead of a finely divided metallic vapor or dust.

The high heat applied to the bottle during the exhausting operationdrives all the occluded gases out of the glass and these are removed, asfar as possible, by the exhaust. The remaining small quantity ofresidual gases is eliminated by chemical combination with the vaporizedmetal.

Since our silvering process is carried out dry, the difficulties due tothe presence of moisture in the old wet silvering process are entirelyeliminated by our invention, in which the formation of the vacuum andthe silver ing are or may be) carried out simultaneously. Whereas theold process required hours for silvering each bottle (including thenecessary baking), our dry silvering process takes only a few minutcstheactual heating of the silvering cage requires only a few seconds.Another advantage is the low cost of magnesium as compared with silver.Therefore, the important practical results of our invention are -first,a material reduction in the manufacturing cost of the cornpleted filler;second, a more efficient bottle on account of the better vacuumobtainable.

Although we have specifically mentioned the metal magnesium for thecoating coil D, other volatile metals or alloys may be used, and ourinvention is not limited to any particular metal, unless otherwisestated in the following metals are applicable, butare too costly forordinar commercial bottles: gold,

silver, barium, ca cium, cerium, ermanium.v

Antimony may be used, but is rittle and rather hard to handle. Metalswhich have too low a melting point to suit present methods of hotexhaust, but which are suitable for cold exhaust are: zinc, cadmium,lead, bisniuth. thallium.

The metal sodium might be used, as its melting point is 97.6 (3;, lessthan three degrees below the boiling point of water. Usually hotliquids, such as coffee or tea, when poured into the bottle, are at alower temperaturethan 100 C. In distilling a metal such as sodium intothe comparatively cooler space between. the two containers, the

sodium is placed in a separate small retort in direct communication withthe evacuated space.

The following metals have too high a boiling point in vacuum forpractical purposes at the present time, but they can be used withcertain precaution, such as close spacing of extremely fine wires;copper, aluminum, nickel, cobalt, tungsten, molybdenum, tantalum, etc.We have produced very fine mirrors of copper, nickel and tungsten.

It will be clear from the preceding explanation and description that thedry silvering process of our invention possesses many materialadvantages over the old wet method and produces a better and cheaperbottle. In its practical application, the basic principle of ourinvention is susceptable of changes and modifications in details ofprocedure, and the specific description heretofore given is not toberegarded in a restrictive sense.

When wespecify magnesium in the claims, we include'pure magnesium andmagnesium alloys. v

What we claim as our invention is:

1. In the manufacture of vacuum receptacles in which an inner and anouter containerof glass are spaced bya vacuum chamber, the process ofcoating the walls of said chamber with a mirror-like surface adapted tominimize the loss of radiant heat from the in- -ner container, whichcomprises vaporizing a closed metallic conductor within a vacuum chamberby heat gener-atedinductively in inseam 2. In the manufacture of vacuumreceptacles in which an inner and an outer contamer of glass are spacedby a vacuum chamber, the process of coating the walls of said in saidconductor by an electric circuit outside of said chamber, said conductorof magnesium beingso arrangedin said chamber that the vaporized metallicmagnesium is deposited on the surrounding glass walls in a substantiallyuniform mirror-like film.

3. In the manufacture of vacuum receptacles in which an inner and anouter container of glass are spaced by a vacuum cham ber, the process ofcoating the walls of said chamber with a mirror-like surface adapted tominimize the loss of radiant heat from the inner container, whichconsists in placing a coil of metallic wire around the inner container,said wire being closed upon itself to form a short-circuited secondarycoil of one or more turns, exhausting the space or chamber between thetwo containers to the re quired vacuum, and inductively subjecting saidwire coil in the evacuated chamber to the action of high-frequencycurrents generated in an electric circuit outside of said vacuum chamberuntil the metal of the wire is vaporized and deposited on thesurrounding walls in a substantially uniform mirror-like film.

4. In the manufature of vacuum receptacles in which an inner and anouter container-of glass are spaced by a vacuum chamber, the process ofcoating the walls of said chamber with a mirror-like surface adapted tominimize the loss of radiant heat from the inner container, whichconsists in placing a coil of magnesium wire around the inner container,said wire being closed upon itself to form a short-circuited secondarycoil of one or more turns. exhausting the space or chamber between thetwo containers to the required vacuum, and inductively subjecting saidwire coil in the evacuated chamber to the action of high-frequencycurrents generated in an electric circuit outside of said vacuum chamberuntil the magnesium of the wire is vaporized and deposited on thesurrounding galls in a substantially uniform mirror-like 5. In themanufacture of vacuum receptacles in which an inner and an outercontainer of glass are spaced by a vacuum chamber, the process ofcoating the walls of said chamber with a mirror-like surface adapted tominimize the loss of radiant heat from the inner container, whichcomprises inductively subjecting a closed metallic coil in said vacuumchamber to the action of high-frequency currents generated in anelectric circuit out- .side of said vacuum chamber until the metal ofthe coil is vaporized and deposited on the surrounding Walls in amirror-like film.

6. In the manufacture of vacuum receptacles in which an inner and anouter con- I tainer of glass are spaced by a vacuum chamas a mirror-likesurface.

7. In the manufacture of vacuum receptacles in which an inner and anouter container of glass are spaced by a vacuum chamber, a closed coilof magnesium wire surrounding the inner container in said vacuumchamber, and electric means wholly outside the vacuum chamber forheating said wire by induced currents until the magnesium is vaporizedand deposited on the surrounding glass walls as a mirror-like surface.

8. In the manufacture of vacuum receptacles in which an inner and anouter container of glass arespaced by a vacuum chamber, a cage or basketof metallic wire surrounding the inner container in said chamher, saidwire cage comprising a plurality of short-circuited secondary coils, aprimary coil surrounding the outer container, and means for passinghigh-frequency currents through said primary coil to heat the wire oftill? said secondary coils until the metal thereof is vaporized anddeposited on the surrounding walls as a mirror-like surface.

9. In the manufacture of vacuum receptacles in which an inner and anouter container of glass are spaced by a vacuum chamher, a coil of metalwire in said chamber arranged to surround the inner-container alongpractically its full length, a portion of the wire of said coilextending across the turns thereof and being connected to said turns soas to provide in effect a plurality of short- ,circuited secondarycoils, and means outside of the vacuum chamber for subjecting said wirecoil or coils to the action of high-frequency currents for vaporizingthe metal of the wire and depositing the same on the sur Eounding wallsin a substantially uniform 10. As a new article of manufacture, adouhie-walled vacuum receptacle in which the walls of the vacuum chamberbetween the inher and outer glass containers are provided with ametallic film formed by the condensation of metal vapor produced by theaction of high-frequency currents, said film uniformly coating saidwalls as a mirror-like surface adapted to prevent the entrance ofradiant heat into said chamber.

11. As a new article of manufacture, a double-walled vacuum receptaclein which the walls of the vacuum chamber between the inner and outerglass containers are provided with a film of magnesium uniformly coatingsaid Walls as a mirror-like surface adapted to prevent the entrance ofradiant heat into said chamber, said film of magnesium being formed bythe condensation of vapor produced by the action of high frequencycurrents on a magnesium wire or strip.

12. In the manufacture. of vacuum receptacles in which an inner and anouter container of glass are spaced by a vacuum chamber, a closed coilof metallic wire surround ing theinner container in said vacuum chamber,spacing members for holding the free end of the inner container firmlyspaced from the outer container, and electric means outside of thevacuum chamber for vaporizing the metal of said wire and depositing thesame on the surrounding walls as a mirrorlike surface, said spacingmember remaining in self-supporting position after the sublimation ofthe metal wire.

13. In the manufacture of vacuum recep tacles in which an inner and anouter container of'glass are spaced by a vacuum chamber, a closed coilof metallic wire surrounding the inner container in said vacuum chamber,beads of soft metal superficially oxidized strung on said coil forholding the free end of the inner container firmly spaced from the outercontainer, and electric means for vaporizing the metal of said Wire anddepositing the same on the surrounding .walls'as a mirror-like surface,said metal beads being held in spacing position by the deposited metalsurrounding them.

14:. As a means for depositing a substantially uniform mirror-likesurface of metal on the glass walls of the vacuum chamber in adouble-walled vacuum receptacle by the vaporizing action of highfrequency currents on a metal, a coil of wire adapted to be inserted insaid chamber around the inner container, said coil consisting of aplurality of turns which are short-circuited by a portion of the wireextending across the turns and being connected thereto, whereby saidcoil becomes in effect a plurality of short-circuited coils.

15. The process of coating the surface of a glass container with asubstantially uniform mirror like film ofmetal, which comprisesarranging a closed coil of wire of the desired metal closely along thesurface to be coated,

6 a ransom 1 to be mirrored, means for evacuating the space containingsaid coil and said surface to the required degree, and meanswholly-outside of said evacuated space for electrically heating saidcoil by induction until the metal pf the wire is vaporized and depositedon the glass surface in a substantially. uniform metallic mirror. L 17.In the manufacture of vacuum recepm tacles in which an inner and anouter container of glass are spaced by a vacuum chamber, the processofcoating the Walls Of said chamber with a mirror-like surface adapted tominimize the loss-of radiant heat from the inner container, whichcomprises subjecting vaporizable metal with said vacuum chamber to heatgenerated by an electric circuit outside of said chamber until the metalis vaporized and deposited in the surrounding glass walls in asubstantially uniform mirror-like film.

18. In the manufacture of vacuum receptacles in which an inner and anouter container of glass are spaced by'a vacuum chamber, the processiofcoating the walls of said chamber with" a mirror-like surface adapted tominimize the loss of radiant heat from the inner container, whichcomprises exhausting said chamber while maintaining the glass receptacleat a high temperature below the soft- 30 emng point of the glass, andvaporizing a closed metallic conductor within the evacuated chamber byheat generated inductively in said conductor by an electric circuitoutside of said chamber,- said conductor being so arranged a that thevaporized metal is deposited on the surrounding lass walls in asubstantially uniform mirror-like film. 19. In the manufacture ofdouble-walled glass vacuum bottles comprising two spaced o containers,meansfor exhausting the annular chamber between the containers whilemaintaining the bottleat a high temperature below the softening oint ofthe glass, a closed coil of av'aporiza 1e metal arranged in said chamberso as to extend practically over the entire inner container, and asource of electric energy outside of said chamber for inductivelyheating said coil untilthe metalthereof isvaporized and deposited as amirror 5 on the surrounding glass walls.

COLING. FINK. JOHN R. BEERS.

